Which DC handles LDAP requests?

Hi,

We have a group here that is writing web apps that use AD for

authentication. Our problem is when they try to authenticate using

LDAP, the request is being thrown all over our domain (rather than the

local subnet). Sometimes it will hit the local DC, other times it

goes to our Mexico site, sometimes over to Maimi, etc. When it goes

to our WAN sites, the web app is timing out.

What determines which domain is servicing the request and is there

anything we can do (aside from hard-coding the DC... due to redundancy

reasons of course)?

Thanks in advance.